Control apparatus for electric power steering system
First Claim
1. A control apparatus for an electric power steering system, said control apparatus comprising:
- steering torque detecting means for detecting a steering torque caused in a steering shaft;
steering force assist command value calculating means for calculating a steering force assist command value which is a target value for controlling a steering assist force caused in the power steering system at least based on the detected steering torque; and
motor controlling means for controlling a current value of a motor for assisting a steering operation based on the calculated steering force assist command value;
wherein the steering force assist command value calculating means comprises calculating means based on a plurality of approximation function equations for approximating a higher order function equation, each of said plurality of approximation function equations coinciding with at least three points of the steering force assist command values corresponding to the steering torques defined by the higher order function equation and calculates the steering force assist command value corresponding to a detected value of the steering torque by the calculating means based on the plurality of approximation function equations.
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Accused Products
Abstract
A steering force assist command value in correspondence with a steering torque is represented by approximation function equations lower than the order of the higher order function equation. The steering torque is sampled at predetermined time intervals and the steering force assist command value in correspondence with the sampled steering torque is calculated by the approximation function equations where when data outputted from a calculation device comprise 16-bit data, upper 8-bit data is outputted to a motor drive circuit and lower 8-bit data is omitted, and the omitted lower 8-bit data is added in calculating operation of next sampling period. An error of the steering force assist command value by omission of the lower 8-bit data is reduced and steering feeling can be improved.
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Citations
10 Claims
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1. A control apparatus for an electric power steering system, said control apparatus comprising:
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steering torque detecting means for detecting a steering torque caused in a steering shaft; steering force assist command value calculating means for calculating a steering force assist command value which is a target value for controlling a steering assist force caused in the power steering system at least based on the detected steering torque; and motor controlling means for controlling a current value of a motor for assisting a steering operation based on the calculated steering force assist command value; wherein the steering force assist command value calculating means comprises calculating means based on a plurality of approximation function equations for approximating a higher order function equation, each of said plurality of approximation function equations coinciding with at least three points of the steering force assist command values corresponding to the steering torques defined by the higher order function equation and calculates the steering force assist command value corresponding to a detected value of the steering torque by the calculating means based on the plurality of approximation function equations. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A control apparatus for an electric power steering system, said control apparatus comprising:
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steering torque detecting means for detecting a steering torque caused at a steering shaft; steering force assist command value calculating means for calculating a steering force assist command value which is a target value for controlling a steering assist force caused at the power steering system at least based on the detected steering torque; and motor controlling means for controlling a current value of a motor for assisting a steering operation based on the calculated steering force assist command value; wherein the steering force assist command value calculating means comprises digital calculation means having a bit number larger than a bit number of the motor controlling means, calculates the steering force assist command value based on data of the steering torque sampled at predetermined time intervals and outputs the calculated steering force assist command value to the motor controlling means in which the steering force assist command value is calculated by adding lower bits data of the steering force assist command value that is omitted in outputting the steering force assist command value to the motor controlling means, to data of the steering torque that is sampled at a next time. - View Dependent Claims (9, 10)
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Specification